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Commit 88c7b2b7 authored by Jens Axboe's avatar Jens Axboe
Browse files

blk-mq: prefetch request in blk_mq_tag_to_rq() 



When drivers or the core calls this function, they usually
dereference the request shortly there after. Prefetch the first
cache line.

Profiling IO workloads shows that this is the most common cache
miss on the block side of things.

Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 8d354f13

block/blk-mq.c

+4 −1
Original line number Diff line number Diff line
@@ -22,6 +22,7 @@ 
#include <linux/sched/sysctl.h>

#include <linux/delay.h>

#include <linux/crash_dump.h>

#include <linux/prefetch.h>



#include <trace/events/block.h>
@@ -588,8 +589,10 @@ EXPORT_SYMBOL(blk_mq_abort_requeue_list); 


struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags, unsigned int tag)

{

	if (tag < tags->nr_tags)

	if (tag < tags->nr_tags) {

		prefetch(tags->rqs[tag]);

		return tags->rqs[tag];

	}



	return NULL;

}